Yiddish: Show a pig a finger and he'll want the whole hand.

SOURCE: Bernstein, Jüdische Sprichwörter und Redensarten.
Variations: replace "pig" with "dog" (hunt|הונט), "devil" (tayvl|טײַוול), or "Jew" or "man" (yidn|ייִדן).

ווײַז אַ חזיר אַ פֿינגער וויל ער די גאַנצע האַנט.

Vayz a khazer a finger vil er di gantse hant.

Show a pig a finger and he'll want the whole hand.